As a device for operating a hand of an industrial robot, there has heretofore been used one in which, as illustrated in FIG. 1, an air cylinder is driven by a fixed pneumatic pressure so as to generate the grasping force of the hand.
In the device for operating the hand of the industrial robot as shown in FIG. 1, a finger-driving mechanism 1 is so constructed as to open or close the finger portions 11 and 12 in accordance with the movement of the piston 31 of the air cylinder 3. Accordingly, the force with which the finger portions 11 and 12 grasp an article to be gripped 2 is determined by the thrust F of the air cylinder 3. This thrust F is given by the following expression: EQU F=S.multidot.P.multidot..eta.
Here, S donotes the pressure-receiving area of the piston, P the pneumatic pressure in the cylinder, and .eta. the efficiency.
Accordingly, the thrust F is uniquely determined by the feed pressure of the air so that the grasping force of the hand becomes constant. Therefore, in the device for operating the hand of the industrial robot as shown in FIG. 1, the article to be gripped 2 is gripped with a constant grasping force which is determined by the feed pressure of the air P. This leads to a problem in which the grasping force cannot be switched in accordance with the state of the article to be gripped, and in some cases the article to be gripped is broken.